The present invention relates generally to phantoms for use in optical and magnetic resonance imaging quality control.
Medical optical imaging is an emerging medical imaging technology. As part of the development of imaging modalities, objects are developed that can be used to test the medical imaging device without the necessity of in vivo scanning. A phantom is a test object that simulates some aspect of the anatomy of interest. These objects are commonly called xe2x80x9ctest phantomsxe2x80x9d or simply xe2x80x9cphantoms.xe2x80x9d In traditional x-ray imaging the phantoms can be as simple as a step-wise increase in thickness of material to simulate higher density. This style phantom is commonly called a step-wedge phantom. In x-ray computed tomography, a phantom filled with water and with circular, cylindrical, or ellipsoidal inclusions is used and one commonly used phantom is referred to as a Shepp-Logan phantom. In x-ray mammography, a standardized mammography phantom is used for federally mandated quality control programs. A good breast phantom permits objective rather than subjective analysis and should be sensitive to small changes in mammographic image quality.
The non-homogeneous nature of breast tissue is difficult to replicate in a medical optical imaging phantom. The refractive index of homogenous materials rules out their use unless their optical properties are modified in some manner. A phantom that can be examined by an accepted imaging method and then imaged by a new method that is being evaluated greatly simplifies the quantitative analysis of the device being tested. In medical optical imaging, a substance called INTRALIPID(trademark) has been widely used to simulate the optical absorption and scattering characteristics of breast tissue. While the use of a INTRALIPID(trademark) as the filler media is of some use, the effects of the container are not controllable. Some researchers use a cylindrical container while other use square or rectangular containers, but none of these configurations resembles an in vivo breast.
A phantom that emulated the optical characteristics of breast tissue, that resembled the breast in shape and size, and that could be scanned by another modality to verify its make up would be of considerable value. The phantom construction technique described herein enables replication of the phantom using routine manufacturing techniques.
It is an object of the present invention to provide a phantom that emulates the optical characteristics of breast tissue, that resembled the breast in shape and size, and that could be scanned by another modality to verify its make up.
It is another object of the present invention to provide a phantom that can be used to evaluate a medical imaging device without the necessity of in vivo scanning.
It is still another object of the present invention to provide a breast phantom that permits objective rather than subjective analysis and is sensitive to small changes in medical optical image quality, to permit the use of the phantom as an integral component of a quality assurance protocol to verify the performance of a medical imaging apparatus being evaluated.
It is another object of the present invention to provide a breast phantom that may be scanned by a magnetic resonance imaging apparatus to generate slice-plane images for direct comparison with those generated by an optical imaging apparatus under evaluation.
It is an object of the present invention to provide a breast phantom having optical characteristics of absorption and scattering that are tissue equivalent to breast tissue.
It is still another object of the present invention to provide a breast phantom that can be replicated by standard manufacturing techniques.
It is still another object of the present invention to provide a breast phantom that is stable over time and whose optical characteristics would not change.
In summary, the present invention provides a breast-shaped phantom for optical imaging comprising a cup in the shape of a human breast in its natural pendant position and a filler occupying the volume of the cup. The cup forms an outer skin of the phantom with a thickness similar to human skin and with optical transparency at selected optical wavelengths similar to human skin. The filler material has optical scattering and absorption characteristics similar to human breast tissue.
The present invention also provides a method for making breast-shaped phantom for optical imaging, comprising the steps of molding a cup in the shape of a breast in a pendant position hanging freely and transversely from the body to form an outer skin of the breast-shaped phantom, the cup having an optical transparency at selected wavelengths similar to human skin; and filling the cup with a filler material with optical scattering and absorption characteristics similar to human breast tissue.
These and other objects of the present invention will become apparent from the following detailed description.